The invention relates to improving reservoir communication within a wellbore.
To complete a well, one or more formation zones adjacent a wellbore are perforated to allow fluid from the formation zones to flow into the well for production to the surface or to allow injection fluids to be applied into the formation zones. A perforating gun string may be lowered into the well and the guns fired to create openings in casing and to extend perforations into the surrounding formation.
The explosive nature of the formation of perforation tunnels shatters sand grains of the formation. A layer of xe2x80x9cshock damaged regionxe2x80x9d having a permeability lower than that of the virgin formation matrix may be formed around each perforation tunnel. The process may also generate a tunnel full of rock debris mixed in with the perforator charge debris. The extent of the damage, and the amount of loose debris in the tunnel, may be dictated by a variety of factors including formation properties, explosive charge properties, pressure conditions, fluid properties, and so forth. The shock damaged region and loose debris in the perforation tunnels may impair the productivity of production wells or the injectivity of injector wells.
One popular method of obtaining clean perforations is underbalanced perforating. The perforation is carried out with a lower wellbore pressure than the formation pressure. The pressure equalization is achieved by fluid flow from the formation and into the wellbore. This fluid flow carries some of the damaging rock particles. However, underbalance perforating may not always be effective and may be expensive and unsafe to implement in certain downhole conditions.
Fracturing of the formation to bypass the damaged and plugged perforation may be another option. However, fracturing is a relatively expensive operation. Moreover, clean, undamaged perforations are required for low fracture initiation pressure (one of the pre-conditions for a good fracturing job). Acidizing, another widely used method for removing perforation damage, is not effective for treating sand and loose debris left inside the perforation tunnel.
A need thus continues to exist for a method and apparatus to improve fluid communication with reservoirs in formations of a well.
In general, according to one embodiment, a tool string for use in a wellbore extending from a well surface comprises a closure member adapted to be positioned below the well surface and a low pressure chamber defined at least in part by the closure member. At least a port is selectively openable to enable communication between the chamber and a wellbore region. The at least one port when opened creates a fluid surge into the chamber to provide a local low pressure condition in the wellbore region. A tool in the tool string is adapted to perform an operation in the local low pressure condition.
In general, according to one embodiment, a tool string for use in a wellbore comprises an assembly having at least a first chamber and a second chamber, and control elements to enable communication with the first chamber to create an underbalance condition in the wellbore and to enable communication with the second chamber to create a flow surge from a formation.
In general, according to another embodiment, a method for use in a wellbore comprises lowering a tool string having a first chamber into the wellbore proximal a formation and activating at least one explosive element to open communication with the chamber to create an underbalance condition in the wellbore proximal the formation.
In general, according to another embodiment, a tool string for use in a wellbore comprises a packer, a circulating valve, and an atmospheric chamber. The circulating valve, when open, is adapted to vent a lower wellbore region below the packer once the packer is set, and the atmospheric chamber is capable of being opened to create an underbalance condition below the packer.
In general, according to another embodiment, an apparatus for use with a wellbore comprises subsea wellhead equipment including a blow-out preventer, a choke line filled with a low density fluid, and a kill line filled with a heavy fluid. A downhole string is positioned below the subsea wellhead equipment, and the choke line is adapted to be open to create an underbalance condition in the wellbore.
In general, according to another embodiment, a method of creating an underbalance condition in a wellbore comprises controlling wellbore pressure at least in a perforating interval to achieve a target level and configuring a perforating gun to achieve a target detonation pressure in the perforating gun upon detonation. An underbalance condition in the perforating interval of the wellbore is created when the perforating gun is shot.
Other or alternative features will become apparent from the following description, from the drawings and from the claims.